THE PRIMARY coaching function in any game is to maximise your own team's strengths and minimise your vulnerabilities while at the same time minimising the opposition's strengths and trying to exploit their vulnerabilities.

And while it's always easier in principle than it is in practice, if I were coaching one of the four preliminary final teams this weekend there are a couple of key strengths I'd be trying to limit in the respective oppositions sides.

First, the Collingwood versus Hawthorn blockbuster on Friday night.

If I was Magpies coach Mick Malthouse setting up for the Hawks I'd be having nightmares about Buddy Franklin burning off the chaser and sprinting through the Hawks' 50m arc or into an open goal.

If there's space to run into, Franklin will attack with devastating effect and will not be run down from behind.

So, regardless of who is playing on Franklin, I'd be making sure there was always a defender goal side of the 2011 All Australian full forward.

If necessary let him push up the field so that he's only getting long shots on goal. That way, to kick four goals from long range he probably needs eight shots. A lot of long shots usually result in a lot of long behinds.

I'm thinking Chris Tarrant is the man for Franklin in a pure shutdown role.

This would leave Ben Reid to play on David Hale, while understanding that he has to be ready to leave Hale and help out on Franklin whenever necessary.

Similarly, Nick Maxwell and Harry O'Brien would be instructed to be ready to jump third-man-up whenever Franklin is involved in a marking contest.

Other defenders, too, and even the midfielders, should be looking to get back and help block the space into which Franklin will lead.

The other big 'must' for Collingwood is to ensure Josh Gibson has to play on an opponent.

Basically Hawthorn's key defenders are vulnerable one-on-one against big, strong-marking forwards, and the Hawks will almost certainly try to use Gibson not as a key position defender but in the same third-up role which he filled so effectively against the Sydney Swans last week, helping out Ryan Schoenmakers and Ben Stratton.

So Collingwood needs to find an opponent for Gibson who will command his full attention.

If he is opposed to Travis Cloke or Chris Dawes, the Pies must be prepared to back their size and strength to win one-out against Gibson, who is not so good when defending a quality big forward.

As stands to reason, if I were Hawks coach Alastair Clarkson planning for the Pies, I'd be looking to do the sorts of things that Collingwood are trying to stop.

If they can't get Gibson into that third-up role, try to use Luke Hodge in the same way.

A huge Hawthorn focus must be to break down the fantastic organisational ability of Maxwell and Shaw in the Collingwood defensive group.

While Clarkson generally likes to play a spare man behind the ball for his own attacking purposes, if he allows that at the opposite end I'd expect the Pies to keep the Hawks to a very low score.

This is where trying not to minimise your own strengths to exploit the opposition's vulnerability becomes a risk-and-reward decision.

It's no easy task to try to generate an extra defender for yourself at one end while making sure the opposition can't do exactly that at the other end, but if Maxwell, Shaw and even O'Brien don't have direct opponents they will completely blunt the opposition scoring.

For Clarkson, keeping forwards in the Hawthorn forward line is in the very high-need category,  so if they push up the ground they must push back very quickly to prevent being outnumbered.

Now, to the Geelong v West Coast game on Saturday.

The No.1 starting point for Geelong against the Eagles is the acceptance that Dean Cox and Nick Naitanui are going to get their hands on the ball in a large percentage of the ruck contests.

As good as Brad Ottens is, the double-team effect will ensure a West Coast dominance in this area, so the Cats will be looking to follow the example of the Collingwood-West Coast game two weeks ago in which the Pies were well beaten in the hit-outs , 50-29, but won the clearances  clearly , 53-31.

The big difference this week is Daniel Kerr. If Geelong is to gain the ascendancy in this area his influence as a stoppage/clearance player must be negated.

Matt Priddis gets big numbers, but his clearances are generally not that penetrating.

Not so Kerr. He moves aggressively through the stoppage and a lot of his touches in-close generate a West Coast surge into open space.

Whether by just blocking the forward release space via a sweeper or getting a body against Kerr to stop his momentum through the stoppage, this is the sort of damaging clearance that Geelong must stop.

Also, getting West Coast full-back Darren Glass out from underneath the long ball kicked deep into the Geelong forward line would be of high priority.

While Eric McKenzie has become a very competent big defender, Glass's immovable presence in the heart of the Eagles' defence is a strength to be nullified.

This means that Geelong's game style from their first final against Hawthorn, in which they ran the ball through the middle of the ground and kicked long into their forward line, won't be nearly as effective. - certainly not if Glass, probably opposed to James Podsiadly, is on the end of it, with Dean Cox floating back into his favourite position deep in the opposition's forward 50 arc.

Ottens, then, must look to work into forward space of his own to force Cox to play as a defensive ruckman. And the Cats must be prepared to vary their delivery into the forward 50 to minimise the Glass/Cox aerial influence.

At the other end of the ground, Geelong's big defenders Tom Lonergan, Harry Taylor and Matthew Scarlett are still the best trio in the game. Long balls into their area will not work even with the Eagles' forward height.

Add Andrew Mackie, Corey Enright and Josh Hunt and the Cats have an experienced, well-organised defensive team. Trying to get them to play on a direct opponent is one of the first priorities. If they are allowed to play team defence scoring against them becomes very difficult and their rebound will become an attacking weapon.

A defensive forward such as Mark Nicoski to stay with Matthew Scarlett and to sneak a goal or two is always a worthwhile start to unsettling Geelong's defensive organisation.

The key midfield starting point for the Eagles will be to minimise the contest-winning impact of Joel Selwood, particularly around the critical centre square clearances.

Younger brother Scott Selwood has been doing a terrific tagging job for the Eagles and would be the logical match-up. The doubt is the uncertain brother versus brother psychology, which should be a consideration in the final decision.

 Older brother Adam Selwood, a possible second option for that match-up, will be sent first to Geelong's Steve Johnson, who when 'on'  is an absolute matchwinner.

Johnson is such an influential player on a good day that his opponent must maintain annoying body contact to test his composure under intense pressure, which at times has been found wanting.

Geelong is looking in good shape, and I think the Cats will beat the Eagles.

Hawthorn, with Franklin and Cyril Rioli, is always a scary opponent because if they both have good matches the Hawks can beat anyone.

Despite the danger of this duo, I think Collingwood, while not as dominant over the last month, will be too strong all over the field and should win.

The views in this article are those of the author and not necessarily those of the AFL or its clubs